1) Field of the Invention
This invention relates to process and apparatus for developing a film, on which an image recorded on an original has been recorded as an electrostatic latent image by charging and subsequent exposure, by feeding a developer to the film.
2) Description of the Related Art
Electrophotographic apparatus have been known which can record an image on a desired frame of an electrophotographic film and can project or copy the thus-recorded image.
In addition, processing heads which are each assembled in an electrophotographic apparatus to apply charging and exposure, development and the like to an electrophotographic film are known in U.S. Pat. Nos. 4,600,291 and 4,697,912, etc.
The processing head disclosed in each of the above patent publication is provided with charging and exposing zone, developing zone, drying zone and fixing zone. These zones are arranged side by side sequentially in the above order along the feeding direction of an electrophotographic film. The arrangement pitch of the individual zones is equal to the frame pitch of the electrophotographic film and is hence constant.
Let's assume that an electrophotographic film is subjected to normal development by the above apparatus. In the charging and exposing zone, the electrophotographic film positioned there, namely, one of the frames of the electrophotographic film is charged positive on the entire surface thereof and then exposed to transmitted or reflected light from an original which is referred as "image light" herein after. Owing to the exposure graphic film is neutralized at areas exposed to the light from the original but remains charged at areas not exposed to the light. As a result, an electrostatic latent image corresponding to the image pattern of the original is formed. In the developing zone, a developer is fed into the spacing between the electrophotographic film and a developing electrode and is allowed flow down through the spacing. Toner particles contained in the developer and charged negative are attracted to the positively charged surface while the developer flows down through the spacing, whereby the electrostatic latent image is made visible. In the drying zone, dry air is blown against the electrophotographic film wetted with the developer so that moisture is eliminated. In the fixing zone, the image is fixed on the electrophotographic film by a fixing lamp or the like.
The quantity of a developer required for the development of an electrostatic latent image formed on an electrophotographic film varies depending on the kind of the original. For example, in the case of an original in which black areas account for a large percentage of the overall image area, in other words, an original whose so-called optical density is high (photographes or contact prints), more toner particles are attracted. In contrast, in the case of an original in which black areas account for a small percentage of the overall image area, in other words, an original whose so-called optical density is low (general characters, drawings, newspapers), less toner particles are attracted. Accordingly, the quantity of the developer to be fed has heretofore been set at a level required for the development of an electrophotographic film exposed to light from an original of a high optical density, and the spacing between the electrophotographic film and a developing electrode has been set to a degree to sufficiently develop the image of the contact prints or the general characters by the quantity of the fed developer. For example, this spacing is set at 0.3-0.4 mm and the developer is fed in a quantity of 0.5 cc or so into the spacing.
When the quantity of the developer and the spacing are set in accordance with conditions for the development of a electrostatic latent image formed as a result of exposure to light from an original of a high optical density, such as a photograph or contact print, in other words, an original requiring toner particles in a large amount as described above, the development of an electrophotographic film exposed to light from an original of a low optical density, such as general characters, a drawing or a newspaper, encounters a problem that toner particles in the developer, said toner particles flowing down apart from the surface of the electrophotographic film, are not attracted onto the electrophotographic film and are allowed to flow away and the utilization factor of the developer is hence low. With a view toward solving this problem, it may be contemplated of reducing the spacing between the electrophotographic film and the developing electrode to improve the utilization factor of the developer. This approach is preferred as the developer can be saved. In addition, the reduced spacing between the developing electrode and the electrophotographic film makes it possible to feed the developer in a small quantity, whereby it is no longer required to recycle any excess developer to the developer bottle, in other words, the developer can be used in accordance with the so-called non-recycling or throw-away system and the processing of the spent developer can be facilitated.
When the spacing between the developing electrode and electrophotographic film is reduced and the quantity of the developer to be fed is reduced as described above, a film with an image of an original of a high optical density formed thereon through charging and exposure may however encounter a potential problem that toner particles may become scarce in absolute quantity because such a film requires lots of toner particles. In this case, the electrostatic latent image cannot be fully rendered visible, thereby resulting in another problem of development blurs.
It has hence been impossible to feed an optimum quantity of a developer to an electrophotographic film in accordance with the optical density of an original.
The problems referred to above arise in both normal and reversal developments.